Plasmid-encoded production of coli surface-associated antigen 1 (CS1) in a strain of Escherichia coli serotype O139.H28

Development and evaluation of genotypic assays for the detection and characterization of enterotoxigenic Escherichia coli

We developed and evaluated a method to genotypically identify enterotoxigenic Escherichia coli (ETEC) and to characterize these organisms with respect to 18 of 21 known colonization factors (CFs). The method, which is based on polynucleotide DNA-DNA colony hybridization, includes a pooled toxin probe assay to identify ETEC, and individual probe assays to detect the enterotoxins STp, STh, and LT, and the CFs CFA/I, CS1-CS8, CS12-CS15, CS17-CS19, CS21, and CS22. We evaluated the pooled toxin probe assay during a cohort study of childhood diarrhea, and the individual probe assays against 33 reference strains and 92 clinical ETEC isolates. There was close to a complete agreement between the pooled toxin probe assay and the individual toxin probe assays, and between the individual CF probe assays and the corresponding phenotypic assays.

Immunological and molecular characterization of Helicobacter felis urease

Urease activity has recently been shown to be an important virulence determinant for Helicobacter pylori, allowing it to survive the low pH of the stomach during colonization. Experimental murine infection with Helicobacter felis is now being used as a model for H. pylori infection to study the effects of vaccines, antibiotics, and urease inhibitors on colonization. However, little information comparing the ureases of H. felis and H. pylori is available. Urease was partially purified from the cell surface of H. felis ATCC 49179 by A-5M agarose chromatography, resulting in an eightfold increase in specific activity over that of crude urease. The apparent Km for urea for the partially purified urease was 0.4 mM, and the enzyme was inhibited in a competitive manner by flurofamide (50% inhibitory concentration = 0.12 microM). Antiserum to whole cells of H. pylori recognized both H. pylori and H. felis urease B subunits. Antiserum raised against H. felis whole cells recognized the large and small autologous urease subunits and the cpn60 heat shock molecule in both H. felis and H. pylori. However, this antiserum showed only a weak reaction with the B subunit of H. pylori urease. Two oligomeric DNA sequences were used as probes to evaluate the relatedness of H. felis and H. pylori urease gene sequences. One 30-mer from the ureA sequence, which had been shown previously to be specific for H. pylori, failed to hybridize to H. felis genomic DNA. A probe to the putative coding sequence for the active site of the H. pylori ureB subunit hybridized at low intensity to a 2.8-kb fragment of BamHI-HindIII-digested H. felis DNA, suggesting that the sequences were homologous but not identical, a result confirmed from the recently published sequences of ureA and ureB from H. felis.

Virulence properties of Escherichia coli strains belonging to serogroups O26, O55, O111 and O128 isolated in the United Kingdom in 1991 from patients with diarrhoea

Some strains of Escherichia coli belonging to serogroups O26, O55, O111 or O128 produce Vero cytotoxin (VT). These serogroups are included in the range of enteropathogenic E. coli (EPEC) serogroups for which commercial antisera are available. In an attempt to obtain information on VT-producing strains other than those of serogroup O157, 122 strains belonging to these four serogroups and isolated in 1991 from patients with diarrhoea in the United Kingdom were tested for hybridization with VT probes. Only 18 of the 122 strains were VT-positive and these were O26 or O128. However 90 strains hybridized with the E. coli attaching and effacing (eae) probe (including 14 VT-positive strains) and 17 with the enteroaggregative E. coli (EAggEC) probe. For 78 eae-positive and 9 EAggEC-positive strains, tissue culture tests correlated with the probe results as the strains gave, respectively, either localized adhesion and a positive fluorescent-actin staining test or a characteristic aggregative attachment. A total of 111 of the 122 strains belonging to serogroups O26, O55, O111 or O128 possessed properties that may be associated with the ability to cause human diarrhoeal disease, and similar studies are needed on strains from the other classical EPEC serogroups.

Characterization of plasmid-borne afa-3 gene clusters encoding afimbrial adhesins expressed by Escherichia coli strains associated with intestinal or urinary tract infections

The afa gene clusters encode afimbrial adhesins (AFA) that are expressed by uropathogenic and diarrhea-associated Escherichia coli strains and belong to a family of hemagglutinins recognizing the Dr blood group antigen as a receptor. This family so far includes AFA-I and AFA-III as well as the Dr and F1845 adhesins (B. Nowicki, A. Labigne, S. Moseley, R. Hull, S. Hull, and J. Moulds, Infect. Immun. 58:279-281, 1990). Reported in this work is the genetic organization of the afa-3 gene cluster cloned from a uropathogenic E. coli strain (A30) which expressed a subtype of AFA designated AFA-III. The amino acid sequence of AFA-III was deduced from the nucleotide sequence of the afaE3 gene and was found to be highly homologous to that of the Dr adhesin (98.1% identity). A polymerase chain reaction assay was developed to detect the presence of afa-3 gene clusters in E. coli strains. Study of the genetic support of the afa-3 gene clusters in the strains which showed positive amplification revealed that they were always located on large, 100-kb plasmids whether the strains originated from patients with cystitis or with diarrhea. Moreover, the cloned afa-3 gene clusters from A30 and from the diarrhea-associated strain AL845 appeared to be carried by 9-kb plasmid regions which displayed a similar genetic organization. Chloramphenicol was reported to be a potent inhibitor of receptor binding by the Dr adhesin (Nowicki et al., Infect. Immun. 58:279-281, 1990). AFA-III expressed by strains AL845 and AL847 appeared to mediate, like the Dr adhesin, chloramphenicol-sensitive hemagglutination, whereas AFA-III produced by A30 conferred chloramphenicol-resistant adherence. A comparison of the sequences of these four proteins indicated that the amino acid at position 52 of the processed AFA could be part of the receptor-binding domain.

A silent regulatory gene cfaD' on region 1 of the CFA/I plasmid NTP 113 of enterotoxigenic Escherichia coli

A DNA sequence, homologous to the cfaD gene of CFA/I region 2, was identified on CFA/I region 1. This sequence is designated cfaD'. It differs from the cfaD gene in containing two deletions and a stop codon. The cfaD' sequence therefore can only encode a truncated CfaD-like protein. The CfaD protein may be a DNA binding protein and functions as a positive regulator of CFA/I fimbriae expression. A regulatory function for the cfaD' is not likely since deletion of the cfaD' sequence does not affect production of CFA/I fimbriae in E. coli K-12 strains. That the cfaD' sequence is present on CFA/I wild-type plasmids isolated from CFA/I strains of different serotypes, obtained at various geographical locations, suggests, however, that this DNA region is not completely without a function.